This invention relates to centrifuge refrigeration systems. Many centrifuges are provided with a refrigeration capability to maintain samples in the centrifuge rotor at a desired low temperature while they are undergoing centrifugation. To achieve the desired cooling, the rotor chamber of the centrifuge is surrounded by refrigeration coils. These coils, which constitute the evaporator in a typical refrigeration system, are supplied with refrigerant through the usual expansion valve which controls the flow of the refrigerant.
While this is conventional practice, a problem encountered with centrifuges is that, due to the usual space limitations in the rotor housing, the expansion valve for the evaporator, if located immediately adjacent the evaporator, is difficult to remove and/or repair. On the other hand, if the expansion valve is located at a distance from the evaporator so that it can be removed or repaired, it can undergo icing and, in any event, the cooling capability of the system is reduced. Both effects are undesirable.
It is known to use a capillary tube or line in lieu of an expansion valve. This delays the expansion of the refrigerant until it reaches the evaporator and hence the loss of the cooling capability is avoided. Unfortunately, a capillary line permits no variable control over the rate of flow of fluid through the evaporator as is provided by the feedback control of the expansion valve. Hence, the mere use of a capillary line is an undesirable solution.